There have been conventionally proposed control apparatuses for recursively identifying the dynamic characteristics of an object to be controlled. The control apparatus has a plant model expressing an object to be controlled by mathematical equations which recursively estimates the parameters of the plant model in such a way as to bring an error between the output of the plant model when an actual control input is applied to the plant model and the output of an actual object to be controlled close to zero. However, when the object to be controlled is a system including significant time delay, the output of the plant model used for identification needs to be an output to an input considering the time delay included by the actual object to be controlled. Moreover, in the case of designing a control apparatus by the use of plant parameters identifying an object to be controlled, which includes time delay, and for controlling the object to be controlled by the control apparatus, it is necessary to design the control apparatus in consideration of time delay in order to achieve performance of high accuracy.
For example, in patent document 1 (U.S. Pat. No. 6,188,953B1), the exhaust system of an internal combustion engine is an object to be controlled, and a plant model for the exhaust system to be controlled is previously constructed in consideration of time delay of a specified constant value of the exhaust system or a specified value set according to the operating state of the internal combustion engine. The parameters of this plant model (parameters to be set at certain values in order to determine the behavior of the model) are identified recursively by the use of output data and input data of the actual object to be controlled. Then, the future output of the exhaust system to be controlled (specifically, output after a specified constant time delay of the exhaust system to be controlled) is estimated recursively by a control apparatus. Moreover, control input is produced by the algorithm of a feedback control by the use of the future output of this exhaust system to be controlled.
Moreover, according to patent document 2 (USP2002-07173901A1), there is provided a control apparatus that performs a feedback control on an input to an object, which is to be controlled and includes a time delay factor, by using such a model for the object to be controlled that expresses the object to be controlled by a transfer function and by predicting the output of the object to be controlled after a lapse of time delay and by comparing a predicted output with a detected output. The control apparatus has a plurality of plant models that are different from each other in time delay. Then, the respective plant models are identified recursively and, of the plurality of plant models, a plant model in which a difference between the predicted output computed by the identified plant model and the actual output becomes minimal is selected as a final model for the object to be controlled.
However, in the case of controlling the object, which is to be controlled which includes time delay, by the use of an identification model, it is necessary to make time delay set in the plant model respond to fluctuations in actual time delay. That is, there is a possibility that the adjusting of the respective parameters by identifying the model will absorb fluctuations in time delay to thereby make it impossible to perform correct identification. In particular, in a system having large fluctuations in the characteristics of the object to be controlled, there are cases where there is a large difference between set time delay and actual time delay. As a result, the object to be controlled is controlled by the use of an identification model absorbing the above-mentioned difference in time delay, which presents a problem of being unable to keep a high degree of control accuracy. Even the patent document 1 in which time delay is set at a specified constant value and even the patent document 2 in which the plant models are identified for a plurality of time delays and in which time delay thought to be closest to an actual time delay is selected as actual time delay cannot be said to express the actual time delay of the object to be controlled. For this reason, both of them have a limit in performing high-accuracy control over the object to be controlled.
The present invention has been made in view of the above-mentioned present circumstances. The object of the present invention is to provide a control apparatus capable of recursively estimating a change in time delay and performing high-accuracy control.